(1) Field of the invention
The present invention has to do with a method for hardening mold parts, that is to say mold cores and hollow mold parts, made of sand with the addition of a binding agent or binding agents able to be hardened by a catalyst, and used for making metal castings.
(2) Prior Art
In this respect the starting point of the invention is a method, whose development I was responsible for, in the case of which a certain amount of a liquid catalyst is put in the mold part with the help of compressed air, with which the catalyst is mixed, and then the mold part is cleared or rinsed with catalyst-free compressed air.
It is important to make certain that there is an even distribution of the mist, produced by mixing catalyst and compressed air, throughout the mold parts, without drops of catalyst being retained on only some of the grains of sand and not transported fully into the remote portions, that is to say all portions of the mold part. For this purpose I made a suggestion of using a heating system for heating the mist evenly before leaving the mixing zone so that the catalyst is changed into a gas. For this reason it is a compressed air-catalyst gas mixture which goes into the mold part. This is something which promotes a quicker movement of the catalyst through the mold part material and, for this reason, a qucker hardening of the mold parts.
However, in comparison, such a manner of operation requires a great amount of energy, because the mist has to be heated up, generally speaking, from the temperature of the compressed air, which is generally between 0.degree. and 20.degree. C., to the temperature for changing the catalyst into its gaseous form, this being necessary every time the mist is forced through to the mold parts.
The starting temperature is normally towards the lower end of the given temperature range, because the compressed air is caused to give up moisture by forcing it through refrigeration dryers. If it is to be heated, it is naturally necessary for heat to be used, for the compressed air in this respect. Furthermore, in this method the heating only takes place during a short time interval in the working step in question so that it is not possible to make certain that in fact there is a complete change of the catalyst into the gas form.